The present invention relates to a method of and apparatus for shaft power generation by the use of an engine. More particularly, the invention pertains to a method of and apparatus for shaft power generation suitable for use in a constant-frequency power generation which is effected by taking out mechanical power from an engine whose number of revolutions varies, such as the main engine of a vessel.
In the shaft power generation method for use in vessels, the main engine for driving a propeller is employed as a mechanical power source, and it is general practice to additionally employ an auxiliary engine such that it is also possible to generate electric power by the auxiliary engine. However, the auxiliary engine is smaller in size and higher in speed than the main engine which has a relatively long stroke and is relatively low in speed, and the auxiliary engine uses fuel oil A, which is of high quality. Therefore, the auxiliary engine is much higher in fuel cost. For this reason, while the main engine is operating, it is efficient and economical practice to take out mechanical power for power generation from the main engine, which is superior to the auxiliary engine in fuel cost. Moreover, it is desirable to operate the auxiliary engine for power generation only on special occasions, for example, when the main engine cannot be operated, or when the vessel is at anchor.
However, the main engine has special characteristics whereby the number of revolutions thereof is not constant but varies incessantly in accordance with the running conditions of the vessel. Therefore, in order to generate electric power of constant frequency, it is necessary to contrive such a means as to constantly maintain the number of revolutions of a power generator at its rated number of revolutions. To obtain a constant rated number of revolutions of the power generator, the eddy current method, the slide clutch method or the thyristor method has hitherto been employed and put into practical use in the case of small-capacity power generation. In the case of large-capacity power generation in a large-sized vessel or the like, however, it is necessary to employ the thyristor method for the sake, for example, of efficiency. As is well known, a thyristor controller has the disadvantage that the cost thereof becomes high in substantially geometric progression as its capacity increases.
Further, since vessels generally have limited space available therein, when a power generation apparatus of the type described above is provided therein, it is desirable that the apparatus should be arranged such as to be as compact as possible so as not to occupy an unnecessarily large space.